1. Field of the Invention
The invention is related to a cellular phone jammer; more particularly, a cellular phone jammer that permits cellular communication in an emergency.
2. Description of Related Art
Due to the wide spread use of cellular phones, they have become very important electronic products to the human life. However, cellular phones are not allowed in many occasions, such as in the hospitals, gas stations, opera halls, and many other performance fields.
Therefore, a cellular phone jammer, claiming to effectively obstruct cellular phone signals within a specific range so as to disable the cellular phone's communication function, is available on the market. U.S. Pat. No. 6,301,475 granted to Saarela, et al. for a “Procedure for limiting the mobility area of a terminal device in a wireless local loop” defines a mobility area (MOA) to perform inhibiting communications in accordance with geographical locations. However, in critical conditions such as a fire accident in a theater, it would cause a tragedy if the cellular phone cannot be used for emergency calls. This is the main reason why the cellular phone jammer is not legal yet in many countries. Therefore, it is desirable to provide a cellular phone jammer to be used ordinarily to effectively inhibit the communication function of the cellular phones, yet to be automatically turned off to allow the communication when there is an emergency within the area.